import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class udpechoServer {

    private DatagramSocket socket = null;

    public udpechoServer (int port) throws SocketException {
        socket = new DatagramSocket(port);
    }


    //通过start启动服务器的核心流程
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while(true){
            //此时通过"死循环"不停处理客户端需求


            //1,读取客户端的请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            //上述收到数据,为二级制byte[]的形式体现的,后续代码如果要进行打印之类的操作
            //需要转成字符串才好处理
            String request = new String(requestPacket.getData(),0,requestPacket.getLength());

            //2.根据请求计算响应,由于此处是回显服务器,响应就是请求
            String response = process(request);
            //3.把响应写回客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(requestPacket);

            //4.打印日志
            System.out.printf("[%s:%d] req = %s, resp=%s\n",requestPacket.getAddress(),requestPacket.getPort(),
                    request,response);

        }
    }

    private String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        udpechoServer server = new udpechoServer(9090);
        server.start();

    }


}
